1. Field of the Invention
The present invention relates to an imaging apparatus, and in particular, to an imaging apparatus that corrects for the effects of flux scattering.
2. Description of the Prior Art
One of the useful properties of photographic film is that it records incident radiant flux in a manner that compresses dynamic range. It has become standard practice to measure the response of photographic film to a given exposure by determining the optical density of the resulting transparency. This is accomplished by illuminating the transparency and measuring the light flux that is transmitted or reflected. Precise measurement of transmitted or reflected flux values when reading transparencies is hampered by technical equipment limitations such as failure to create even illumination in the plane of the transparency, vignetting, optical misalignment, and sensor nonuniformity. Some prior art devices have attempted to correct for these limitations, such as the device disclosed in Jansson et al., "Implementation and application of a method to quantitate 2-D gel electrophoresis patterns", Electrophoresis 4, 82-91 (1983).
The measurement of transmitted or reflected flux values may also be hampered by other factors such as scattering of flux due to dust on the optical elements, scattering of flux due to imperfections in the optical system, and scattering of flux from the transparency itself.
Various attempts have been made to use optical isolation to eliminate or reduce the contribution of scattered flux due to these above-listed scattering phenomena while measuring the flux transmitted through a transparency. An instrument known as a digital scanning microdensitometer is used to scan an entire image on a transparency, pixel by pixel, to convert it to a series of numbers or to a digitized image. This form of the data is useful for subsequent image processing and analysis. Scanning can be accomplished by planar motion of a stage containing the transparency, or alternately, rotation of a drum having the transparency thereon. Such a device, however, requires troublesome mechanical parts that demand a high level of precision, limit the speed of the scan, render the scanner cost high, and produce wear that limits the life of the equipment. As a result, the cost of such a device is excessive.
Methods and apparatus that correct for resolution distortion in spectrometers and other optical devices are summarized in Jansson, "Deconvolution: With Applications in Spectroscopy", Academic Press (1984).
In view of the foregoing it is believed advantageous to obtain the speed and convenience of a relatively low cost scanner, yet at the same time obtain the precision and accuracy that attends the use of isolation to eliminate the effects of scattered flux.